This invention relates to a hydraulic binder product and a method of manufacturing the product which can be used in various applications such as acoustic, thermal insulation and fire protection panels in buildings, fire resistant coatings on substrates or structures and in the binding or sealing of earthworks or ore bodies.
Gypsum boards used for wall and ceiling boards are manufactured by pouring a slurry of gypsum in water, often with other additives, onto a moving sheet of specially manufactured paper. The slurry is leveled either before or after being overlaid with another sheet of paper which is then side wrapped whereafter the gypsum is dried. The disadvantage is the cost of the paper and the cost of removing the considerable quantities of water necessary for the slurry consistency. Other gypsum wall boards without paper liners, are manufactured, some by adding a cellulous fibre to the gypsum, to which is added water, and which is then pressed, usually between double belt presses.
Asbestos fibre cement building boards were previously manufactured by the Hatcheck method in which asbestos fibre was suspended in an aqueous suspension of cement and silica particles. The cement and silica coated asbestos fibre was then removed by dewatering sheets from the bath and placed on a dewatering table. Successive sheets were then pressed together to achieve the required thickness, and after a dwell time of some fourteen hours, the boards were then autoclaved. Shapes were made by draping the dewatered sheets over shape formers such as corrugated metal templates. Subsequent to the identification of the health hazards of asbestos fibre, these have been largely replaced by cellulous fibre from pulp, sometimes mixed with synthetic fibres. An alternative cementitious building board is made from cement-bound wood chips which are pressed at high pressure, clamped and then autoclaved.
The disadvantage of these methods is either the expense of the equipment or the slow processes involved.
It is also known to make foamed products from hydraulic binders such as gypsum and international publication number WO 99/28266 teaches a method of making a composite product by mixing a hydraulic binder, finely divided lignocellulosic fibres and water, optionally containing a polyvinyl alcohol to form a paste, introducing a foam generated from a polyvinyl alcohol into the paste and mixing to form a foamed product, forming the foamed product into a desired shape and allowing the hydraulic binder to set to form a composite product.
International publication number WO 01/14284 described a method of making a composite product by mixing a hydraulic binder and water in an amount sufficient to form a paste, introducing a foam into the paste, the foam being generated from a mixture of polyvinyl alcohol solution and a second hydrophilic polymer, mixing to form a foamed product, forming the foamed product into a desired shape and allowing the hydraulic binder to set to form the composite product.
It is important that the density of the binder products be uniform during manufacturing. In certain applications it is desirable that the binder product be of a specific shape, rigidity or of varying thickness. In order to manufacture certain products or in order to use the binder product for certain applications it is important that the product is tack-free or non-sticky during manufacture.